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Network Working Group                                           R. Droms
Internet-Draft                                             Cisco Systems
Expires: April 24, 2003                                 October 24, 2002


            A Guide to Implementing Stateless DHCPv6 Service
               draft-droms-dhcpv6-stateless-guide-01.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 24, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   Stateless DHCPv6 service is used by hosts to obtain configuration
   information such as the addresses of DNS servers that does not
   require the maintenance of any dynamic state for individual clients.
   A host that uses stateless DHCP must have obtained its IPv6 addresses
   through some other mechanism, typically stateless address
   autoconfiguration.  This document is a guide to the protocol messages
   and options that must be implemented to provide stateless DHCPv6
   service.

1. Introduction

   Hosts that have obtained IPv6 addresses through some other mechanism



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   can use stateless DHCPv6 to obtain other configuration information
   such as a list of DNS server or NTP servers.  A stateless DHCPv6
   server provides only configuration information to hosts and does not
   perform any address assignment.  Such a server is called "stateless"
   because it need not maintain any dynamic state for individual
   clients.

   While the DHCPv6 specification [3] defines more than 10 protocol
   messages and 20 options, only a subset of those messages and options
   are required for stateless DHCPv6 service.  This document gives
   guidelines about which messages and options are required for
   stateless DHCPv6 service.  The intended use of the document is to
   guide the efficient and complete implementation of clients and
   servers that use stateless DHCPv6 service.

   The operation of relay agents is the same for stateless and stateful
   DHCPv6 service.  The operation of relay agents is described in the
   DHCPv6 specification.

   Section 4 of this document lists the sections of the DHCPv6 document
   that an implementor should read for an overview of the DHCPv6
   specification and the basic requirements of a DHCPv6 service.
   Section 5 lists the specific messages and options that are
   specifically required for stateless DHCPv6 service.  Section 6
   describes how stateless and stateful DHCPv6 servers interact to
   provide service to clients that require address assignment and
   clients that require only stateless service.

2. Terminology

   Throughout this document, "DHCP" refers to DHCP for IPv6.

   This document uses the terminology defined in RFC2460 [1], the DHCP
   specification, the DHCP DNS configuration options specification [4]
   and the DHCP NTP configuration options specification [5]..

   "Stateless DHCP" refers to the use of DHCP to provide configuration
   information to clients that does not require the server to maintain
   dynamic state about the DHCP clients.

3. Overview

   This document assumes that a host using stateless DHCP configuration
   is not using DHCP for address assignment, and that a host has
   determined at least a link-local address as described in section 5.3
   of RFC2461 [2]

   To obtain configuration parameters through stateless DHCP, a host



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   uses the DHCP Information-request message.  DHCP servers respond to
   the host's message with a Reply message that carries the DNS
   configuration parameters.  The Reply message from the server can
   carry configuration information such as a list of DNS servers and NTP
   servers.

4. Basic Requirements for Implementation of DHCP

   Several sections of the DHCP specification [3] provide background
   information or define parts of the specification that are common to
   all implementations:

   1-4 -   give an introduction to DHCPv6 and an overview of DHCP
      message flows

   5 -     defines constants used throughout the protocol specification

   6, 7 -  illustrates the format of DHCP messages

   8 -     describes the representation of Domain Names

   9 -     defines the "DHCP unique identifier" (DUID) used to identify
      DHCP participants

   13-16 - describe DHCP message transmission, retransmission and
      validation

   21 -    describes authentication for DHCP


5. Implementation of stateless DHCP

   The client indicates that it is requesting configuration information
   by sending an Information-request message that includes an Option
   Request option specifying the options that it wishes to receive from
   the DHCP server.  For example, if the client is attempting to obtain
   DNS configuration information, it includes either or both of the DNS
   configuration options in the Information-request message.  The server
   determines the appropriate configuration parameters for the client
   based on its configuration policies and responds with a Reply message
   containing the requested parameters.  In this example, the server
   would respond with DNS configuration parameters.

   Use of the Client DUID option and the Server DUID option are not
   required for stateless DHCP service.  However, it can be beneficial
   for the client to include a client DUID option, because the server
   administrator may want to customize the server's response on a per-
   client basis, and this requires that the client identify itself.



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5.1 Messages required for stateless DHCP

   Clients and servers implement the following messages for stateless
   DHCP service; the section numbers in this list refer to the DHCPv6
   specification:

   Information-request: sent by a DHCP client to a server to request DNS
      configuration parameters (sections 18.1.5 and 18.2.5)

   Reply:               sent by a DHCP server to a client containing the
      DNS configuration parameters (sections 18.1.6 and 18.2.8)

   In addition, servers and relay agents implement the following
   messages for stateless DHCP service:

   Relay-forward: Sent by a DHCP relay agent to carry the client message
      to a server (section 15.13)

   Relay-reply:   Sent by a DHCP server to carry a response message to
      the relay agent (section 15.14)


5.2 Options required for stateless DHCP service

   Clients and servers implement the following options for stateless
   DHCP service; the section numbers in this list refer to the DHCPv6
   specification:

   Option Request: specifies the configuration information that the
      client is requesting from the server (section 22.7)

   Status Code:    used to indicate completion status or other status
      information (section 22.13)

   Servers and relay agents implement the following options for
   stateless DHCP service; the section numbers in this list refer to the
   DHCPv6 specification:

   Client message: Sent by a DHCP relay agent in a Relay-forward message
      to carry the client message to a server (section 20)

   Server message: Sent by a DHCP server in a Relay-reply message to
      carry a response message to the relay agent (section 20)

   Interface-ID:   Sent by the DHCP relay agent and returned by the
      server to identify the interface to use to forward a message to
      the client (section 22.18)




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5.3 Options used for configuration information

   Clients and servers use the following options to pass configuration
   information to clients:

   DNS Server:      specifies the DNS servers the client uses for name
      resolution; see "DNS Configuration options for DHCPv6"

   DNS search list: specifies the domain names to be searched during
      name resolution; see "DNS Configuration options for DHCPv6"

   NTP Servers:     specifies the NTP servers the client uses for
      synchronizing its clock; see "Time Configuration Options for
      DHCPv6"


5.4 Other options used in stateless DHCP

   Clients and servers may implement the following options for stateless
   DHCP service; the section numbers in this list refer to the DHCPv6
   specification [3]:

   Preference:     Sent by a DHCP server to indicate the preference
      level for the server (section 22.8)

   Elapsed time:   Sent by a DHCP client to indicate the time since the
      client began the DHCP configuration process (section 22.9)

   User Class:     Sent by a DHCP client to give additional information
      to the server for selecting configuration parameters for the
      client (section 22.15)

   Vendor Class:   Sent by a DHCP client to give additional information
      about the client vendor and hardware to the server for selecting
      configuration parameters for the client (section 22.16)

   Vendor-specific Information: Sent by a DHCP server to pass
      information to clients in options defined by vendors (section
      22.17)

   Client DUID:    Sent by a DHCP client to identify itself (section
      22.2).  Clients are not required to send this option; servers
      never send this option

   Authentication: Used to provide authentication of DHCP messages
      (section 21)





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6. Interaction with DHCP for Address Assignment

   In some networks, there may be both clients that are using stateless
   address autoconfiguration and DHCP for DNS configuration and clients
   that are using DHCP for stateful address configuration.  Depending on
   the deployment and configuration of relay agents, DHCP servers that
   are intended only for stateless configuration may receive messages
   from clients that are performing stateful address configuration.

   A DHCP server that is only able to provide stateless configuration
   information through an Information-request/Reply message exchange
   discards any other DHCP messages it receives.  Specifically, the
   server discards any messages other than Information-Request or Relay-
   forward it receives, and the server does not participate in any
   stateful address configuration messages exchanges.  If there are
   other DHCP servers that are configured to provide stateful address
   assignment, one of those servers will provide the address assignment.

7. Acknowledgments

   Ted Lemon, Bernie Volz and Jim Bound reviewed this document and
   contributed editorial suggestions.

References

   [1]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
        Specification", RFC 2460, December 1998.

   [2]  Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
        IP Version 6 (IPv6)", RFC 2461, December 1998.

   [3]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", draft-ietf-dhc-dhcpv6-27 (work in progress), October
        2002.

   [4]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms, "DNS Configuration options for DHCPv6", draft-ietf-dhc-
        dhcpv6-opt-dnsconfig-01 (work in progress), October 2002.

   [5]  Vijayabhaskar, A., "Time Configuration Options for DHCPv6",
        draft-ietf-dhc-dhcpv6-opt-timeconfig-00 (work in progress),
        February 2002.

   [6]  Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
        November 1998.





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Author's Address

   Ralph Droms
   Cisco Systems
   300 Apollo Drive
   Chelmsford, MA  01824
   USA

   Phone: +1 978 497 4733
   EMail: rdroms@cisco.com









































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Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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